The electrical systems in today's motor vehicles are equipped with a multiplicity of electrical loads, a substantial portion of which are used for implementing added-convenience functions. The power consumption of such vehicle electrical systems may be considerable even in stationary mode, depending on the load, which in the worst case can result in complete discharge of the vehicle battery. Of particular importance in this context, besides the power consumption of the individual electrical loads, is the power consumption of the bus system in the vehicle electrical system. This is because today's bus systems are usually designed such that waking up a load entails waking up the entire system, which significantly increases power consumption.
One of the above added-convenience functions is what is known as the “keyless entry function”. A common feature of known keyless entry systems is that there is provision for an, in particular radio-based, authentication dialog between a motor-vehicle-end keyless entry control unit and a user-end radio key or the like in order to check the access authorization of the user. Following a successful authentication dialog and possibly further operator control events, the motor vehicle is unlocked and/or, depending on the design, possibly a hatch or the like is operated by a motor.
A known arrangement having a keyless entry function (DE 103 33 894 A1) provides for the keyless entry control unit to continuously or cyclically test whether a radio key is present for the authentication dialog. Since this is associated with accordingly continuous or cyclic discharge of the vehicle battery, it is proposed that an additional energy store be provided for the keyless entry function.
In order to reduce the power consumption of the electrical system in a motor vehicle, it has also been proposed that at least part of the control unit be intermittently transferred to a power-saving standby mode and be woken into an operating mode according to the situation (DE 10 2004 027 541 A1). A challenge for this method is the correct switching between the standby mode and the operating mode, namely such that the respectively desired function is not impaired nor is there any susceptibility to external influences or misuse.
A known arrangement having a keyless entry function (DE 20 2005 020 140 U1) is equipped with a sensor arrangement which has an associated sensor element in the form of a proximity sensor. Waking the keyless entry control unit and possibly opening a hatch or the like by motor are initiated in this case by an operator control event which is performed by the user of the motor vehicle. The operator control event may be the user approaching the motor vehicle, a foot movement or the like. This method is the basis for the present invention.